JP2008249842A - Zoom lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which is suitable for an interchangeable lens attachable to a single lens reflex camera for silver halide film and a digital single lens reflex camera, which secures a wide viewing angle compatibly with a long lens back, whose various aberrations are satisfactorily corrected, and whose performance degradation due to an assembly error is restrained, and to provide an imaging apparatus using the zoom lens. <P>SOLUTION: The zoom lens 1 includes the first lens group GR1 having negative refractive power, the second lens group GR2 having positive refractive power, the third lens group GR3 having negative refractive power, and the fourth lens group GR4 having positive refractive power, which are located in order from an object side to an image surface side, and performs zooming by moving the respective groups when varying power from a wide angle end to a telephoto end. The zoom lens 1 has a cemented lens of three lenses constituted of a lens G12 having negative refractive power, a biconvex lens G13 having positive refractive power, and a lens G14 having negative refractive power, which are located in order from the object side to the image surface side, in the fourth lens group. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel zoom lens and an imaging apparatus. Specifically, a zoom lens suitable for an interchangeable lens that can be mounted on a single-lens reflex camera for a silver salt film or a digital single-lens reflex camera, and a zoom lens capable of sufficiently securing a lens back, and an image pickup apparatus using the zoom lens About.

  Due to the recent increase in the number of pixels of photoelectric conversion elements, there is a demand for higher performance in the photographic optical system, and there is also a demand for zoom lenses that have a bright F number and include a super wide field angle. Furthermore, in the interchangeable lens for a single-lens reflex camera, there is a restriction that a sufficient lens back must be secured in addition to the above-described requirements.

  As conventional techniques, for example, in Patent Document 1, in order from the object side to the image surface side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a first lens group having a negative refractive power. There has been proposed an ultra-wide-angle zoom lens having a four-group zoom configuration in which a three-lens group and a fourth lens group having a positive refractive power are arranged to set the angle of view at the wide-angle end to 122 degrees.

JP 2005-106878 A

  However, in the super wide-angle zoom lens disclosed in Patent Document 1, the effective diameter on the object side becomes very large, and the F number is as dark as about 5.6 at the telephoto end. The demand for bright numbers is not fulfilled.

  In view of the above-mentioned problems, the present invention can achieve both a wide angle of view and a long lens back suitable for an interchangeable lens that can be mounted on a single-lens reflex camera for silver salt film or a single-lens reflex camera for digital use. It is an object of the present invention to provide a zoom lens in which aberration correction is satisfactorily performed and performance deterioration due to an assembly error is reduced, and an imaging apparatus using the zoom lens.

  A zoom lens according to an embodiment of the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a negative refractive power, which are sequentially arranged from the object side to the image plane side. In the zoom lens that includes a third lens group and a fourth lens group having positive refractive power, and performs zooming by moving each group during zooming from the wide-angle end to the telephoto end, the fourth lens group includes: The lens has a negative refractive power, a biconvex lens having a positive refractive power, and a three-piece cemented lens composed of a lens having a negative refractive power, which are positioned in order from the object side to the image plane side.

  An imaging apparatus according to an embodiment of the present invention includes a zoom lens according to the present invention and an image sensor that converts an optical image formed by the zoom lens into an electrical signal.

  According to the present invention, both a wide angle of view and a long lens back can be achieved, various aberrations can be corrected well, and performance degradation due to assembly errors can be reduced.

  The best mode for carrying out the zoom lens and the imaging apparatus of the present invention will be described below with reference to the drawings.

  First, the zoom lens of the present invention will be described.

  The zoom lens according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, which are sequentially positioned from the object side to the image plane side. A zoom lens comprising a fourth lens group having a positive refractive power, and performing zooming by moving each group during zooming from the wide-angle end to the telephoto end, and in the fourth lens group from the object side The lens has a negative refractive power, a biconvex lens having a positive refractive power, and a three-piece cemented lens composed of lenses having a negative refractive power, which are sequentially arranged toward the image plane side.

  In the zoom lens of the present invention, by adopting a zoom type of negative positive and negative, it is possible to achieve both a wide angle of view and a long lens back, and in the fourth lens group, using a surface having a strong curvature, It is possible to satisfactorily correct spherical aberration and off-axis coma. That is, the surface having a strong curvature has high position sensitivity, and the performance is significantly fluctuated by a slight misalignment or inclination, which requires a high assembling system and causes an increase in cost. Therefore, in the zoom lens of the present invention, the position sensitivity is reduced by using a surface having a strong curvature as a cemented surface in the cemented lens, and the occurrence of errors during assembly is reduced, thereby simplifying the lens barrel structure. It is possible to do.

  The fourth lens group has a positive refractive power. Therefore, in order to make the combined refractive power of the fourth lens group positive, a lens group having positive refractive power is required in addition to the three-piece cemented lens having negative refractive power. The Petzval aberration generated in the first lens group can be corrected by increasing the positive refractive power of the positive lens (group) in the fourth lens group. It makes it difficult to correct aberrations. Therefore, a negative lens in the fourth lens group is a three-piece cemented lens, and a positive lens (group) in the fourth lens group is generated by including a positive lens having a strong curvature in the three-piece cemented lens. It is possible to increase the refractive power of the positive lens (group) while satisfactorily correcting spherical aberration and astigmatism. By making the three-piece cemented lens negative and positive, it is possible to suppress the refraction of strong light rays and to realize good Petzval correction and chromatic aberration correction.

In the zoom lens according to the embodiment of the present invention, it is preferable that the following conditional expressions (1) and (2) are satisfied.
(1) 0.3 <Ld1-Ld2 <0.65
(2) 23 <| Nd1-Nd2 | <74
However,
Ld1: Refractive index of the lens closest to the object side of the third cemented lens in the fourth lens group Ld2: Refractive index of the second lens from the object side of the three cemented lens in the fourth lens group Nd1: Fourth lens group Abbe number Nd2 of the lens on the most object side of the three-piece cemented lens in the middle: The Abbe number of the second lens from the object side of the three-piece cemented lens in the fourth lens group.

  Satisfying these conditional expressions (1) and (2) makes it possible to achieve both sagittal flare correction and axial chromatic aberration correction over the entire zoom range.

  If it is out of the range defined by the conditional expression (1), the sagittal flare increases. On the other hand, the chromatic aberration increases when the value is out of the range defined by the conditional expression (2).

  In the zoom lens according to an embodiment of the present invention, it is desirable that the three-piece cemented lens has an aspheric surface formed so that the positive refractive power becomes weaker as the distance from the optical axis increases. Furthermore, it is desirable that the aspherical surface in the three-piece cemented lens is located closest to the image plane side.

  By having the aspheric surface in the three-piece cemented lens, coma aberration and spherical aberration can be corrected well. In addition, it is more effective in correcting aberrations to dispose an aspherical surface on the most image side.

The aspheric surface formed in the three-piece cemented lens preferably satisfies the following conditional expression (4).
(4) −30 <(| x | − | x0 |) / (c0 × (N′−N) × f4) <− 0.1
However,
x: aspheric surface shape x0: aspherical reference spherical shape c0: curvature of aspherical reference spherical surface N: refractive index of aspherical object-side medium N ′: refractive index f4 of aspherical image-side medium f4: The focal length of the first lens group.

  If conditional expression (4) is satisfied, off-axis coma aberration and spherical aberration on the telephoto side can be corrected satisfactorily. If the upper limit value of conditional expression (4) is exceeded, the power of the aspheric surface becomes too strong, and it becomes difficult to correct spherical aberration on the telephoto side. If the lower limit value of conditional expression (4) is not reached, the power of the aspheric surface becomes too weak and it becomes difficult to correct off-axis coma.

Further, it is desirable that the biconvex lens in the three-piece cemented lens satisfies the following conditional expression (5).
(5) −0.5 <(Rpf + Rpr) / (Rpf−Rpr) <0.5
Rpf: radius of curvature of the object side surface of the biconvex lens in the triplet cemented lens Rpr: radius of curvature of the image side surface of the biconvex lens in the triplet cemented lens.

  Conditional expression (5) is a conditional expression for defining the shape of the biconvex lens in the three-piece cemented lens in the fourth lens group. If conditional expression (4) is satisfied, spherical aberration, coma, astigmatism, and axial chromatic aberration can be corrected in a balanced manner.

In the zoom lens according to an embodiment of the present invention, the fourth lens group includes a positive lens group located on the object side of the three-piece cemented lens, and satisfies the following conditional expression (3): It is desirable.
(3) -3.0 <f3n / fp <-0.1
However,
f3n: focal length of the three-piece cemented lens in the fourth lens group fp: focal length of the positive lens group located on the object side of the three-piece cemented lens in the fourth lens group.

  By having a positive lens group on the object side of the three-piece cemented lens, coma and image plane can be favorably corrected. Further, the conditional expression (3) defines the focal length ratio between the three-piece cemented lens and the positive lens group on the object side. If the upper limit value of the conditional expression (3) is exceeded, the power of the positive lens group is determined. Becomes weaker, leading to an increase in the radial size of the fourth lens unit. On the contrary, if the lower limit value of conditional expression (3) is not reached, the power of the positive lens group becomes strong, the sensitivity to the error in the distance between the positive lens group and the three-piece cemented lens becomes too strong, and high incorporation accuracy. Is required.

  Next, specific embodiments of the zoom lens of the present invention and numerical examples in which specific numerical values are applied to the embodiments will be described with reference to the drawings and tables.

  In each embodiment, an aspherical surface is introduced, and the aspherical shape is defined by the following equation (1).

In Equation 1, x is the distance in the optical axis direction from the apex of the lens surface, y is the height in the direction perpendicular to the optical axis, c is the paraxial curvature at the apex of the lens surface, ε is the conic constant, A ⁱ is the i th aspherical coefficient.

  FIG. 1 shows a lens configuration at the wide-angle end of the zoom lens 1 according to the first embodiment, and arrows indicate movement trajectories on the optical axis toward the telephoto end of each lens group.

  The zoom lens 1 includes, in order from the object side to the image plane side, a first lens group GR1 having a negative refractive power, a second lens group GR2 having a positive refractive power, a third lens group GR3 having a negative refractive power, The fourth lens group GR4 having a positive refractive power is arranged.

  The first lens group GR1 is positioned in order from the object side to the image plane side, and has a negative lens G1 having an aspheric surface on the object side and a concave surface having a strong curvature on the image plane side, and a strong curvature on the image plane side. An object-side sub-group composed of a negative lens G2 having a concave surface, an image-side sub-group composed of a negative lens G3 having an aspheric surface on the object side, a negative lens G4, and a positive lens G5. Composed. The second lens group GR2 includes a cemented lens of a negative lens G6 and a positive lens G7, and a positive lens G8, which are sequentially positioned from the object side to the image plane side. The third lens group GR3 is composed of a cemented lens of a negative lens G9 and a positive lens G10, which are sequentially positioned from the object side to the image plane side. The fourth lens group GR4 includes, in order from the object side to the image plane side, a three-piece cemented lens including a positive lens G11, a negative lens G12, a positive lens G13, and a negative lens G14 having an aspheric surface on the image plane side. It comprises a positive lens G15. An aperture stop S is positioned on the object side of the second lens group GR2, and an image plane side subgroup including the third lens G3, the fourth lens G4, and the fifth lens G5 in the first lens group GR1 is included. Move on the optical axis for focusing.

  Table 1 shows lens data of Numerical Example 1 in which specific numerical values are applied to the zoom lens 1 according to the first embodiment. In Table 1 and other tables showing lens data, “surface number” indicates the i-th surface counted from the object side, and “curvature radius” indicates the paraxial axis of the i-th surface from the object side. The radius of curvature, “axis top surface spacing” is the shaft top surface spacing between the i-th surface and the (i + 1) -th surface, and “refractive index” is the d-line (wavelength = 587.6 nm (wavelength = 587.6 nm The refractive index in nanometers)), “Abbe number” indicates the Abbe number in the d-line of the glass material having the i-th surface on the object side, and “*” after the surface number i indicates that the surface is aspherical “Di” indicates that the distance between the shaft upper surfaces is a variable interval.

  During zooming from the wide-angle end to the telephoto end, the distance d10 between the first lens group GR1 and the second lens group GR2 (aperture stop S), and the distance d16 between the second lens group GR2 and the third lens group GR3. In addition, the distance d19 between the third lens group GR3 and the fourth lens group GR4 changes. Therefore, in the numerical example 1, the wide-angle end (f = 15.40), the intermediate focal length (f = 23.25) and the telephoto end (f = 33.99) between the wide-angle end and the telephoto end of the intervals d4, d10, d16 and d19. ) Are shown in Table 2 together with the focal length f, F number Fno, and angle of view 2ω. The distance d4 between the object side sub group and the image plane side sub group in the first lens group GR1 changes during focusing.

  The object side surface (first surface) of the first lens G1, the object side surface (fifth surface) of the third lens G3, and the image surface side surface (25th surface) of the fourteenth lens G14 are aspherical. Therefore, Table 3 shows the aspheric coefficients of the surfaces in Numerical Example 1 together with the conic constant ε.

  2 to 4 show spherical aberration, astigmatism, and distortion in the infinite focus state of Numerical Example 1, FIG. 2 is at the wide angle end, FIG. 3 is at the intermediate focal length, and FIG. The aberrations at the telephoto end are shown. In the spherical aberration diagram, the vertical axis represents the ratio to the open F value, the horizontal axis defocused, the solid line is the d line, the broken line is the C line (wavelength = 656.3 nm), and the alternate long and short dash line is the g line (wavelength = Represents the spherical aberration at 435.8 nm). In the astigmatism diagram, the vertical axis represents the image height, the horizontal axis represents the focus, the solid line represents the sagittal, and the broken line represents the meridional image plane. In the distortion diagram, the vertical axis represents the image height and the horizontal axis represents%.

  FIG. 5 shows the lens configuration at the wide-angle end of the zoom lens 2 according to the second embodiment, and arrows indicate the movement trajectory on the optical axis toward the telephoto end of each lens group.

  The zoom lens 2 includes, in order from the object side to the image plane side, a first lens group GR1 having a negative refractive power, a second lens group GR2 having a positive refractive power, a third lens group GR3 having a negative refractive power, The fourth lens group GR4 having a positive refractive power is arranged.

  The first lens group GR1 is positioned in order from the object side to the image plane side, and has a negative lens G1 having an aspheric surface on the object side and a concave surface having a strong curvature on the image plane side, and a strong curvature on the image plane side. An object-side sub-group including a negative lens G2 having a concave surface, an image-side sub-group including a negative lens G3 having an aspheric surface on the object side, and a positive lens G4. The second lens group GR2 includes a cemented lens of a negative lens G5 and a positive lens G6, and a positive lens G7, which are sequentially positioned from the object side to the image plane side. The third lens group GR3 is composed of a cemented lens of a negative lens G8 and a positive lens G9, which are sequentially positioned from the object side to the image plane side. The fourth lens group GR4 includes, in order from the object side to the image surface side, a three-lens cemented lens including a positive lens G10, a negative lens G11, a positive lens G12, and a negative lens G13 having an aspheric surface on the image surface side. It comprises a positive lens G14. An aperture stop S is located between the second lens group GR2 and the third lens group GR3, and an image plane side subgroup consisting of the third lens G3 and the fourth lens G4 in the first lens group GR1. Moves on the optical axis for focusing.

  Table 4 shows lens data of Numerical Example 2 in which specific numerical values are applied to the zoom lens 2 according to the second embodiment.

  During zooming from the wide-angle end to the telephoto end, the distance d8 between the first lens group GR1 and the second lens group GR2, and the distance d13 between the second lens group GR2 and the third lens group GR3 (aperture stop S). In addition, the distance d17 between the third lens group GR3 and the fourth lens group GR4 changes. Therefore, at the wide-angle end (f = 10.22), the intermediate focal length (f = 15.43) between the wide-angle end and the telephoto end, and the telephoto end (f = 23.32) of the intervals d8, d13, and d17 in Numerical Example 2. Each value is shown in Table 5 together with the focal length f, F number Fno, and angle of view 2ω. The distance d4 between the object side sub group and the image plane side sub group in the first lens group GR1 changes during focusing.

  The object side surface (first surface) of the first lens G1, the object side surface (fifth surface) of the third lens G3, and the image surface side surface (23rd surface) of the thirteenth lens G13 are aspherical. Therefore, Table 6 shows the aspheric coefficients of the above surfaces in Numerical Example 2 together with the conic constant ε.

  6 to 8 show spherical aberration, astigmatism, and distortion in the infinite focus state of Numerical Example 2, FIG. 6 is at the wide angle end, FIG. 7 is at the intermediate focal length, and FIG. The aberrations at the telephoto end are shown. In the spherical aberration diagram, the vertical axis represents the ratio to the open F value, the horizontal axis represents defocus, the solid line represents the d-line, the broken line represents the C line, and the alternate long and short dash line represents the spherical aberration. In the astigmatism diagram, the vertical axis represents the image height, the horizontal axis represents the focus, the solid line represents the sagittal, and the broken line represents the meridional image plane. In the distortion diagram, the vertical axis represents the image height and the horizontal axis represents%.

  FIG. 9 shows the lens configuration at the wide-angle end of the zoom lens 3 according to the third embodiment, and arrows indicate the movement trajectory on the optical axis toward the telephoto end of each lens group.

  The zoom lens 3 includes, in order from the object side to the image plane side, a first lens group GR1 having a negative refractive power, a second lens group GR2 having a positive refractive power, a third lens group GR3 having a negative refractive power, The fourth lens group GR4 having a positive refractive power is arranged.

  The first lens group GR1 is positioned in order from the object side to the image plane side, and has a negative lens G1 having an aspheric surface on the object side and a concave surface having a strong curvature on the image plane side, and a strong curvature on the image plane side. An object-side sub-group including a negative lens G2 having a concave surface, an image-side sub-group including a negative lens G3 having an aspheric surface on the object side, and a positive lens G4. The second lens group GR2 includes a cemented lens of a negative lens G5 and a positive lens G6, and a positive lens G7, which are sequentially positioned from the object side to the image plane side. The third lens group GR3 is composed of a cemented lens of a negative lens G8 and a positive lens G9, which are sequentially positioned from the object side to the image plane side. The fourth lens group GR4 includes, in order from the object side to the image plane side, a three-lens cemented lens including a positive lens G10, a negative lens G11, a positive lens G12, and a negative lens G13 having an aspheric surface on the image plane side, It comprises a positive lens G14. The aperture stop S is positioned on the object side of the second lens group GR2, and the image side sub-group consisting of the third lens G3 and the fourth lens G4 in the first lens group GR1 moves on the optical axis. And do focusing.

  Table 7 shows lens data of Numerical Example 3 in which specific numerical values are applied to the zoom lens 3 according to the third embodiment.

  During zooming from the wide-angle end to the telephoto end, the distance d8 between the first lens group GR1 and the second lens group GR2 (aperture stop S) and the distance d14 between the second lens group GR2 and the third lens group GR3. In addition, the distance d17 between the third lens group GR3 and the fourth lens group GR4 changes. Therefore, at the wide-angle end (f = 10.22), the intermediate focal length (f = 15.43) between the wide-angle end and the telephoto end, and the telephoto end (f = 23.32) of the intervals d8, d14, and d17 in Numerical Example 3. Each value is shown in Table 8 together with the focal length f, F number Fno, and angle of view 2ω. The distance d4 between the object side sub group and the image plane side sub group in the first lens group GR1 changes during focusing.

 The object side surface (first surface) of the first lens G1, the object side surface (fifth surface) of the third lens G3, and the image surface side surface (23rd surface) of the thirteenth lens G13 are aspherical. Therefore, Table 9 shows the aspheric coefficients of the above surfaces in Numerical Example 3 together with the conic constant ε.

  10 to 12 show spherical aberration, astigmatism, and distortion in the infinite focus state in Numerical Example 3, FIG. 10 is at the wide angle end, FIG. 11 is at the intermediate focal length, and FIG. The aberrations at the telephoto end are shown. In the spherical aberration diagram, the vertical axis represents the ratio to the open F value, the horizontal axis represents defocus, the solid line represents the d-line, the broken line represents the C line, and the alternate long and short dash line represents the spherical aberration. In the astigmatism diagram, the vertical axis represents the image height, the horizontal axis represents the focus, the solid line represents the sagittal, and the broken line represents the meridional image plane. In the distortion diagram, the vertical axis represents the image height and the horizontal axis represents%.

  FIG. 13 shows the lens configuration at the wide-angle end of the zoom lens 4 according to the fourth embodiment, and arrows indicate the movement trajectory on the optical axis toward the telephoto end of each lens group.

  The zoom lens 4 includes, in order from the object side to the image plane side, a first lens group GR1 having a negative refractive power, a second lens group GR2 having a positive refractive power, a third lens group GR3 having a negative refractive power, The fourth lens group GR4 having a positive refractive power is arranged.

  The first lens group GR1 is positioned in order from the object side to the image plane side, and has a negative lens G1 having an aspheric surface on the object side and a concave surface having a strong curvature on the image plane side, and a strong curvature on the image plane side. An object-side sub-group composed of a negative lens G2 having a concave surface, an image-side sub-group composed of a negative lens G3 having an aspheric surface on the object side, a negative lens G4, and a positive lens G5. Composed. The second lens group GR2 includes a cemented lens of a negative lens G6 and a positive lens G7, and a positive lens G8, which are sequentially positioned from the object side to the image plane side. The third lens group GR3 includes a negative lens G9, and a cemented lens of the negative lens G10 and the positive lens G11, which are positioned in order from the object side to the image plane side. The fourth lens group GR4 includes, in order from the object side to the image plane side, a three-piece cemented lens including a positive lens G12, a negative lens G13, a positive lens G14, and a negative lens G15 having an aspheric surface on the image plane side. It comprises a positive lens G16. An aperture stop S is positioned on the object side of the second lens group GR2, and an image plane side subgroup including the third lens G3, the fourth lens G4, and the fifth lens G5 in the first lens group GR1 is included. Move on the optical axis for focusing.

  Table 10 shows lens data of a numerical example 4 in which specific numerical values are applied to the zoom lens 4 according to the fourth embodiment.

  During zooming from the wide-angle end to the telephoto end, the distance d10 between the first lens group GR1 and the second lens group GR2 (aperture stop S), and the distance d16 between the second lens group GR2 and the third lens group GR3. Further, the distance d21 between the third lens group GR3 and the fourth lens group GR4 changes. Therefore, at the wide-angle end (f = 16.42), the intermediate focal length (f = 24.01) between the wide-angle end and the telephoto end, and the telephoto end (f = 34.01) of the intervals d10, d16, and d21 in Numerical Example 4. Each value is shown in Table 11 together with the focal length f, F number Fno, and angle of view 2ω. The distance d4 between the object side sub group and the image plane side sub group in the first lens group GR1 changes during focusing.

  The object side surface (first surface) of the first lens G1, the object side surface (fifth surface) of the third lens G3, and the image surface side surface (27th surface) of the fifteenth lens G15 are aspherical. Therefore, Table 12 shows the aspheric coefficients of the above surfaces in Numerical Example 4 together with the conic constant ε.

  14 to 16 show spherical aberration, astigmatism, and distortion in the infinite focus state in Numerical Example 4, FIG. 14 is at the wide angle end, FIG. 15 is at the intermediate focal length, and FIG. The aberrations at the telephoto end are shown. In the spherical aberration diagram, the vertical axis represents the ratio to the open F value, the horizontal axis represents defocus, the solid line represents the d-line, the broken line represents the C line, and the alternate long and short dash line represents the spherical aberration. In the astigmatism diagram, the vertical axis represents the image height, the horizontal axis represents the focus, the solid line represents the sagittal, and the broken line represents the meridional image plane. In the distortion diagram, the vertical axis represents the image height and the horizontal axis represents%.

  Table 13 below shows values corresponding to the conditional expressions (1) to (5) in the numerical examples 1 to 4.

  Numerical Examples 1 to 4 satisfy the conditional expressions (1) to (5), respectively, and as shown in the respective aberration diagrams, the intermediate focal length between the wide angle end and the telephoto end, and the telephoto end, as shown in each aberration diagram In FIG. 5, each aberration is corrected with good balance.

  Next, the imaging apparatus of the present invention will be described.

  An imaging apparatus according to the present invention includes a zoom lens and an imaging element that converts an optical image formed by the zoom lens into an electrical signal, and the zoom lens is positioned in order from the object side to the image plane side. A first lens group having power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, from the wide-angle end to the telephoto end. During zooming, each group is moved to perform zooming, and in the fourth lens group, a lens having a negative refractive power, which is located in order from the object side to the image plane side, has a birefringent positive refractive power. And a three-piece cemented lens composed of a lens having negative refractive power.

  Therefore, in the imaging apparatus of the present invention, a wide field angle and a long lens back are compatible, and the fourth lens group uses a surface with a strong curvature to correct spherical aberration and off-axis coma. A zoom lens that makes it possible to perform the above-mentioned operations well.

  Next, a specific embodiment of the imaging apparatus of the present invention is shown in a block diagram in FIG.

  The digital camera 10 is configured as a so-called single-lens reflex camera with interchangeable lenses. The digital camera 10 is used by detachably attaching the lens unit 20 to a camera body 30 having an image pickup device.

  The lens unit 20 includes a zoom lens or a single focus lens, a drive unit that drives each part of these lenses, and a control unit that drives and controls the drive unit, and the above-described zoom lens of the present invention can be used as the lens. That is, it is possible to use the zoom lenses 1 to 4 shown in the above-described embodiments and their numerical examples, or the zoom lenses of the present invention implemented in forms other than those shown in the above-described embodiments and numerical examples. When the lens is a zoom lens 21, a predetermined lens group, for example, a zoom driving unit 22 that moves each lens group during zooming, and a predetermined lens group, for example, an image plane side sub-element in the first lens group during focusing. Each drive unit includes a focus drive unit 23 that moves the group and an iris drive unit 24 that changes the aperture diameter of the aperture stop, and a lens control CPU (Central Processing Unit) 25 that controls the drive of each drive unit.

  The camera body 30 includes an image sensor 31 that converts an optical image formed by the zoom lens 21 into an electrical signal. In addition, a flip-up mirror 32 is disposed in front of the image sensor 31, and the light from the zoom lens 21 is guided to the pentaprism 33, and further from the pentaprism 33 to the eyepiece lens 34. The photographer can view the optical image formed by the zoom lens 21 through the eyepiece lens 34.

  For example, a CCD (Charge Coupled Device), a CMOS (Complementary Metal-Oxide Semiconductor), or the like can be applied to the imaging element 31. The electrical image signal output from the image pickup device 31 is subjected to various processes by the image processing circuit 35, and then data compression is performed by a predetermined method and is temporarily stored in the image memory 36 as image data.

  A camera control CPU (Central Processing Unit) 37 controls the entire camera body 30 and lens unit 20 in an integrated manner, takes out image data temporarily stored in the image memory 36, and stores it in the liquid crystal display device 38. It is displayed or saved in the external memory 39. Also, the image data stored in the external memory 39 is read and displayed on the liquid crystal display device 38. Signals from the operation unit 40 such as a shutter release switch and a zooming switch are input to the camera control CPU 37, and each unit is controlled based on the signals from the operation unit 40. For example, when the shutter release switch is operated, a command is issued from the camera control CPU 37 to the mirror driving unit 41 and a command is issued to the timing control unit 42, and the mirror driving unit 41 causes the flip-up mirror 32 to be shown by a two-dot chain line in the figure. The light beam from the zoom lens 21 is input to the image sensor 31 and the signal read timing of the image sensor is controlled by the timing controller 42. The camera body 30 and the lens unit 20 are connected by a communication connector 43, and signals relating to the control of the zoom lens 21, such as an AF (Auto Focus) signal, an AE (Auto Exposure) signal, and a zooming signal, are transmitted to the camera control CPU 37. To the lens control CPU 25 via the communication connector 43, and the zoom control unit 22, the focus drive unit 23, and the iris drive unit 24 are controlled by the lens control CPU 25, and the zoom lens 21 enters a predetermined state.

  In the above embodiment, the imaging apparatus is shown as a single-lens reflex camera, but it may be applied as a fixed lens type camera. Further, the present invention can be applied not only to a digital camera but also to a silver salt film camera.

  In addition, the shapes and numerical values of the respective parts shown in the above embodiments are merely examples of specific embodiments for carrying out the present invention, and these limit the technical scope of the present invention. It should not be interpreted.

It is a figure which shows the lens structure of 1st Embodiment of this invention zoom lens. FIG. 3 and FIG. 4 show aberration diagrams of Numerical Example 1 in which specific numerical values are applied to the first embodiment. This diagram shows spherical aberration, astigmatism, and distortion at the wide angle end. It shows spherical aberration, astigmatism and distortion at the intermediate focal length. It shows spherical aberration, astigmatism, and distortion at the telephoto end. It is a figure which shows the lens structure of 2nd Embodiment of this invention zoom lens. FIG. 7 and FIG. 8 show aberration diagrams of Numerical Example 2 in which specific numerical values are applied to the second embodiment. This drawing shows spherical aberration, astigmatism, and distortion at the wide angle end. It shows spherical aberration, astigmatism and distortion at the intermediate focal length. It shows spherical aberration, astigmatism, and distortion at the telephoto end. It is a figure which shows the lens structure of 3rd Embodiment of this invention zoom lens. FIG. 11 and FIG. 12 show aberration diagrams of Numerical Example 3 in which specific numerical values are applied to the third embodiment. This diagram shows spherical aberration, astigmatism, and distortion at the wide angle end. It shows spherical aberration, astigmatism and distortion at the intermediate focal length. It shows spherical aberration, astigmatism, and distortion at the telephoto end. It is a figure which shows the lens structure of 4th Embodiment of the zoom lens of this invention. 15 and 16 show aberration diagrams of Numerical Example 4 in which specific numerical values are applied to the fourth embodiment. This drawing shows spherical aberration, astigmatism, and distortion at the wide-angle end. It shows spherical aberration, astigmatism and distortion at the intermediate focal length. It shows spherical aberration, astigmatism, and distortion at the telephoto end. It is a block diagram which shows one Embodiment of this invention imaging device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Zoom lens, GR1 ... 1st lens group, GR2 ... 2nd lens group, GR3 ... 3rd lens group, GR4 ... 4th lens group, G12 ... Lens with negative refractive power, G13 ... Biconvex shape and positive G14: lens having negative refractive power, 2 ... zoom lens, GR1 ... first lens group, GR2 ... second lens group, GR3 ... third lens group, GR4 ... fourth lens group, G11: a lens having a negative refractive power, G12: a lens having a biconvex shape and a positive refractive power, G13: a lens having a negative refractive power, 3 ... a zoom lens, GR1 ... a first lens group, GR2 ... a second Lens group, GR3... Third lens group, GR4... Fourth lens group, G11... Lens having negative refractive power, G12... Biconvex lens having positive refractive power, G13. 4 ... Zoomle GR1 ... first lens group, GR2 ... second lens group, GR3 ... third lens group, GR4 ... fourth lens group, G13 ... lens having negative refractive power, G14 ... biconvex shape and positive refractive power G15: Lens having negative refractive power, 10: Imaging device, 21: Zoom lens, 31 ... Imaging element

Claims (6)

A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a positive refractive power, which are located in order from the object side to the image plane side. In a zoom lens that includes a fourth lens group and performs zooming by moving each group during zooming from the wide-angle end to the telephoto end,
The fourth lens group includes, in order from the object side to the image surface side, a lens having a negative refractive power, a biconvex lens having a positive refractive power, and a lens having a negative refractive power. A zoom lens comprising three cemented lenses. The zoom lens according to claim 1, wherein the following conditional expressions (1) and (2) are satisfied.
(1) 0.3 <Ld1-Ld2 <0.65
(2) 23 <| Nd1-Nd2 | <74
However,
Ld1: Refractive index of the lens closest to the object side of the third cemented lens in the fourth lens group Ld2: Refractive index of the second lens from the object side of the three cemented lens in the fourth lens group Nd1: Fourth lens group Abbe number Nd2 of the lens on the most object side of the three-piece cemented lens in the middle: The Abbe number of the second lens from the object side of the three-piece cemented lens in the fourth lens group. 2. The zoom lens according to claim 1, further comprising an aspherical surface formed such that a positive refractive power decreases as the distance from the optical axis increases in the three-piece cemented lens. The zoom lens according to claim 3, wherein the aspherical surface in the three-piece cemented lens is positioned closest to the image plane side. 2. The zoom lens according to claim 1, wherein the fourth lens group includes a positive lens group positioned on the object side of the three-piece cemented lens, and satisfies the following conditional expression (3).
(3) -3.0 <f3n / fp <-0.1
However,
f3n: focal length of the three-piece cemented lens in the fourth lens group fp: focal length of the positive lens group located on the object side of the three-piece cemented lens in the fourth lens group. An imaging apparatus comprising a zoom lens and an image sensor that converts an optical image formed by the zoom lens into an electrical signal,
The zoom lens includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, which are positioned in order from the object side to the image plane side. 4th lens group having a refractive power of 2 ×, and when zooming from the wide-angle end to the telephoto end, zooming is performed by moving each group, and the zoom lens is positioned in order from the object side to the image plane side in the fourth lens group. An imaging apparatus comprising: a lens having negative refractive power; a biconvex lens having positive refractive power; and a three-piece cemented lens including a lens having negative refractive power.

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